A method of calculating a line passing through a neighborhood of the center in a hollow organ (hereinafter referred to as “core line”) and successively displaying virtual endoscope images along the core line (for example, patent document 1) is known as an image display method for enabling efficient diagnosis of the inside of a hollow organ such as a large bowel, bronchial tubes, blood vessels, etc. However, when a hollow organ having folds such as a large bowel or the like is observed, the back side of a fold becomes a blind area in the virtual endoscope display, and thus there is a probability that a lesion is overlooked.
An image obtained by slicing open a hollow organ in a longitudinal direction (hereinafter referred to as “panoramic image”) is known as another image display method for observing a hollow organ. The panoramic image is obtained, for example, by setting each point on a core line (hereinafter referred to as “observing point”) as a light source, radially radiating rays (virtual light beams) in a luminal wall direction within a cross-section on which a directional vector of the core line at an observing point position is set as a normal vector, thereby performing ray-casting, and performing rendering processing (for example, patent document 2). According to this method, as compared with a case where a virtual endoscope image is observed along a core line in a forward direction, a blind area caused by a structure such as a fold or the like can be reduced.